Google is set to launch in-application billing for Android next week, and is encouraging developers to upload their billing-event-enabled apps now.

The Android Marketplace has been talking about in-application billing for almost a year now, and yesterday the team finally opened the store to developer testing with a view to launching commercially next week. In the meantime it's Android Marketplace only.

Apple's iTunes platform got in-application billing a while back, and even customers of Nokia's Ovi store can pay extra to get an Eagle to backup for their Angry Birds, but Android users have been left out until now. So from next week applications purchased from the Android Marketplace will be able to trigger chargeable events from within the application.

It's worth noting that this is a feature of the Android Marketplace, not the Android platform - other application stores, such as Amazon's recently launched alternative, will have to make their own arrangements and sell them to developers.

Developers are desperate to get in-app billing, as the "insert coin to continue" model is considered the holy grail of revenue generation. Some of the latest iPhone games (such as Craneballs Studio's Overkill) are entirely dependent on the capability to sell the player guns and ammunition, the game itself being free. But in the Android world in-application billing offers the store a differentiator too.

Google's Android Marketplace will now have a feature other app stores don't, and one in which developers will invest time and effort. Google will also be hoping to integrate the system into billing systems run by the local network operator too, for simplicity, though that's not happening as fast as some had hoped

But adding this kind of functionality increases store loyalty, and motivates other application stores to emulate the functionality as well as pushing Google to innovate further. That's the idea at least, and a laudable ideal, but still a lot more complicated than the Apple approach of just owning everything. ®